Method of tanning leather and the leather produced by said method



Patented July 23, 1935 UNITED STATES PATENT OFFICE METHOD OF TANNING LEATHER AND THE LEATHER PRODUCED BY SAID METHOD Sven H. Friestedt, Roselle Park, J.

No Drawing. Application September 14, 1934, Serial No. 744,013 I 18 Claims. (01. 149-5) This invention relates to manufacture of tanning processes; and it also comprises the leather produced by the said process, this leather being at least partially tanned by bringing it into contact with croton aldehyde or a derivative thereof and being characterized by being very soft, absorbing water readily, drying out without hardening, taking dyestuffs in even level shades and being incapable of being resolved into its component parts by chemical or physical treatment; all as more fully hereinafter set forth and as claimed.

Of the various types of leathers produced by commercial tanning processes, none has more desirable properties for many purposes than that resulting from the oil tanning or chamoising process. by oil tanning is The so-called chamois leather produced very soft. It absorbs water readily, which makes it desirable for washing purposes and it dries out soft after being wet.

The leather is also very stable and resistant to dilute acids and alkalis.

One of the few disadvantages possessed by oil tanned leather is that it cannot be dyed in level and pleasing colors since it s method of producfrizzing or by splitting. is expensive, laborious and The oil tanning process time consuming, the

operation usually taking about 3,-weeks. It requires large amounts of marine animal oils.

But

in spite of these unfavorable factors chamois leather is still produced by the ancient art of oil tanning chiefly due to the fact that no entirely satisfactory substitute has process.

been found for this Of course various substitutes have been proposed for the oil tanning has come into commercial hyde process.

process. One which use is the formalde- Formaldehyde has been found to have a precipitating and preservative effect on hide substance and leather produced with the use of this agent has many properties in common with chamois. However formaldehyde is apparently not a true tanning produced by this process is agent since leather not stable. For example, upon warmmg with dilute acid,- it is readily converted back int formaldehyde and raw hide substance. The limitations of such a leather are obvious.

It has been proposed at various times to employ other aldehydes for tanning leather but none of these processes have come into commercial use. It has been the consensus of opinion in the industry that higher aldehydes are unsatisfactory for tanning purposes. It has been reported that these higher aldehydes require prohibitively long periods of time to produce any tanning action.

I have now found that skins can be satisfactorily tanned within a few hours time by, exposing them to the action of croton aldehyde. This procedure produces a leather which possesses all the desirable properties of oil dressed leather, such as being soft, water absorbent and stable. But in addition the new leather can be readily dyed in even level shades. Moreover the process is capable of use in producing many kinds of leather other than chamois since the skins or hides can be tanned without removing the grain. The new process is not expensive. It therefore overcomes the principal limitations of the oil tanning process.

In conducting the new process it is only necessary to prepare skins or hides for tanning by conventional processes and then to expose them to the action of croton aldehyde, usually in a slightly alkaline aqueous solution. The leather thus produced is then finished by conventional methods.

The new process can be combined with any of the conventional tanning processes, such as the formaldehyde process, the tawingprocess or the chrome process. For example, the skins can either first be partially tanned with say 4 per cent formaldehyde, then washed out and the tannagecompleted with croton aldehyde, or they can first be partially tanned with croton aldehyde and the tannage can then be completed with formaldehyde.

In another combined process the skins can first be tanned with croton aldehyde either completely or partially, washed out and given a retannage with alum, aluminum sulphate, basic aluminum 4 sulphate or any other aluminum salt. Or this retannage may be given after the skins have been fat-liquored or after they have been fat-liquored and dried out, the skins being wet back prior to the retannage.

When the croton aldehyde method oftanning is to be combined with the chrome process, the skins can be partially tanned-with basic chromic salts either before or after tannage with croton aldehyde. The chrome tannage is sufficiently permanent to withstand the action of the alkaline solution which is usually employed in croton aldehyde tanning. In this case therefore the leather can be tanned with basic chromic salts in the usual way and retanned with croton aldehyde, or after a chrome tannage it may be fat-liquored and then retanned with croton aldehyde. Or after the chrome tannage and fat-liquoring it can be dried out, wet back and then retanned. On the other hand the leather can first be tanned either partially or completely with croton aldehyde, washed out and immediately retanned with basic chromic salts or first fat-liquored and then retanned or dried out after the fat-liquoring, then wet down and retanned with the basic chromic salt.

It is also possible to combine the croton aldehyde tanning process with the various vegetable tan-- ning processes by methods which will be obvious to those skilled in the art. The particular combination of processes chosen, will depend upon the type of leather used and the properties desired.

In a specific embodiment of my invention I took 100 pounds of pickled sheepskins with the grain layer removed and degreased them with kerosene in the well-known manner. After degreasing, I depickled the skins in a tanners drum or rocker containing a solution consisting of 200 pounds water, 10 pounds Glauber's salt and 5 pounds borax. The skins were introduced into this solution and the drum was rotated for minutes, when all mineral acids from the pickling were found to the neutralize The skins, after depickling as above, were drained in a slotted box for an hour or two, this time being utilized for the preparation in the rocker of a bath containing the following inedients:

Pounds Water 200 Borax 6 Glaubers salt 10 Soda ash 3 The skins were introduced into this bath and rotation of the drum was started.

I then dissolved 8 pounds of croton aldehyde in water and this was gradually added to the drum over a period of 5 hours, during which the drum was continuously rotated. The tanned skins were well washed in running water. They were of a yellowish creamy color, well tanned, and with standing 9. temperature of 185 F. without curling. The tanned skins were then dyed in the usual manner with the dye known as fast brown, after which they were fat-liquored or stufled with sulfonated castor oil and finally finished in sistant to dilute acids the usual manner.

The leather obtained in the above manner was found to be in every dressed or chamois leather. It was very soft, re-

it-absorbed water readily and dried out without hardening. It-was dyed in an even level shade.

While not desiring to be limited to any theory of the reaction involved in my tanning process, it is my present'belief that the unsaturated group of the croton aldehyde; as well as the aldehyde group itself, unites in some manner or condenses with the collagen molecule, possibly with certain union of the croton aldehyde with the hide subbe much-more permanent than any similar union which may take place with formaldehyde.- This indicates that the unsatuway comparable with oil and alkalie's and, when wet,

The procedure outlined in the above specific embodiment can, of course, be varied to a con-- siderable extent without departing from the scope of the present invention. The above process can be combined with any-of the conventional tanning processes as outlined previously. Other types of skins may be used and various kinds of leather may be produced. This is due to the fact that skins or hides can be satisfactorily tanned without removing the grain. Thus, all kinds of glove, garment, shoe, furniture, roller, belt and automobile leather can be tanned by my process. Croton aldehyde is thus practically a universal tanning agent; In all cases the leathers produced are stable, soft and water absorbent, and all are capable of being dyed in level shades.

The leathers produced by my process can be finished either with the grain on, on the grain side for glazed kid (goat skins), box calf (calf skins) and side leather or furniture or automobile leathers (hides or kips) or on the fieshside for ooze or suede leathers. On the other hand, after removing the grain, the leather may be finished for chamois, buck skins, mocha leather and fieshers or suedes. Also the skivers (or the split off grain layer) can be tanned separately, or the skiver can be split off after tannage.

The solutions in the depicklin'g and in the tanning baths can be varied to a considerable extent. Many diiferent alkaline metal salts can be employed in varying concentrations in these baths, such as phosphates, bi-carbonates, lactates, acetates, etc. It is advantageous, however, to maintain a pH in the tanning bath ranging from about 8.5 to 10. It is desirable to employ a solution which is sufllciently well buffered so that the pH does not fall below a value of about ,8 during the tanning operation. I have found that croton aldehyde tans best in slightly alkaline solutions within the above pH range.

The amount of croton aldehyde required in the tanning step varies, of course, with the leather to be tanned. An average value is about 8 per cent based on the weight of the hides. This figure varies from about 6 to 9 per cent with different types ofhides. The time required for tanning varies with the concentration and amount of croton aldehyde hours with 5 hours as about the average.

The temperatures employed during thetanning process can be varied widely. It is best, however, to start with a bath temperature of about to F. During the process such temperatures usually rise to from to F. due to the heat generated by rotation of the drum and from the heat of reaction.

Leather produced by my process may be dyed with any of the usual leather dyes. Examples are leather brown, orange T and anthracene chrome yellow. In all cases even level. shades are produced, as mentioned previously.

Various derivatives of croton employed in my process. The croton aldehyde may be substituted with halogen, alkyl, alkoxy, hydrocarbon, etc., groups, for example. Among useful compounds there may be mentioned the Skins may e .tanned with croton aldehyde employed and with the type of skins, etc. It usually requires from about 3 to 7,

aldehyde may be in the vapor state if desired. Sufllcient croton aldehyde is vaporized by blowing warm air through a body of the same. These vapors may then be passed through a rotating drum containing moist pelts in condition for tanning. The pelts may be taken directly from a depickling bath for example. Such pelts retain suflicient of the alkaline liquor to produce a favorable pH value during tannage.

Other modifications of my process which fall within the scope of the following claims will be immediately evident to those skilled in the art.

What I claim is:

1. In the process of manufacturing leather, the step which comprises subjecting hide substance to the action of an aldehyde selected from a class consisting of croton aldehyde and its derivatives.

2. In the manufacture of leather, theprocess which comprises preparing skins for tanning,

subjecting the so-prepared skins to the action of an aqueous solution of croton aldehyde, and finishing. I

3. The process of claim 2 wherein the said aqueous solution is slightly alkaline.

4. The process of claim 2 wherein the said aqueous solution has a pH ranging from about 8.5 to 10. i 5. The process of claim 2 wherein the said aqueous solution is buffered to maintain the same at a pH above 8 during the tanning process.

6. The process which comprises tanning a skin with croton aldehyde and dyeing the same.

'7. In the manufacture of chamois leather, the process which comprises freeing a skin from the grain layer, preparing it for tanning by usual methods, subjecting it to the action of croton aldehyde, fat-liquoring and finishing.

8. In the manufacture of chamois leather, the

. process which comprises freeing a skin from the grain layer, preparing it for tanning by a process including a pickling step. depickling, subjecting it to the action of a slightly alkaline aqueous solution of croton aldehyde; fat-liquoring and finishing.

9. In the manufacture of leather the process which comprises at least partially tanning a skin by one of the usual tanning processes and combining this procedure with a step wherein the skin is subjected to the action of croton aldehyde.

10. The process of claim 9 wherein the usual 5 tanning process precedes the tanning with croton aldehyde.

11. The process of claim 9 wherein the usual tanning process follows the tanning with croton aldehyde. 10

12. In the process of manufacturing leather, the step which comprises contacting a skin with a slightly alkaline aqueous, solution containing about 8 per cent of croton aldehyde, as based on the weight of the skin.

13. In the process of manufacturing leather, the step which comprises subjecting a skin to a slightly alkaline buffered solution of croton aldehyde at a temperature ranging from about 90 to 130 F. V i 2 14. In the process of manufacturing leather, the step which comprises subjecting a skin to a slightly alkaline buffered solution of croton aldehyde at a temperature ranging from about 90 to 130 F. and for a period ranging from about 3 25 to '7 hours. I

15. As a new product, a skin in combination with an aldehyde selected from a class consisting of croton aldehyde and its derivatives, the said product being stable and taking dyes in even level 30 shades.

, 16. As a new product, a skin in combination with one of the usual tanning agents and also" combined with an aldehyde selected from a class consisting of croton aldehyde and its derivatives.

17. A new chamois leather comprising a skin free from its grain layer and in combination with l croton aldehyde, said leather being characterized by being soft, absorbing ,water readily, drying without hardening, being resistant to dilute acids 40 and alkalis and dyeing ineven level shades.

18. As a new product, a skin in combination with croton aldehyde and dyed in an even level shade.

svEri, FRIESTEDT. 

